1. Field of the Invention
The present invention relates to bus ways for electrical distribution systems, and more particularly, to such systems that include three phases and neutral conductor with paired phase arrangement.
2. Description of the Related Art
It has been well established in the art of designing polyphase (mostly three-phase systems) power distribution systems that the use of bus ways with paired phase arrangements for the bus conductors provides significant advantages in conduction efficiency, reduced impedance and balanced voltage drop for unbalanced loads. For a discussion on the paired phase conductor effect, refer to AIEE 54-329, Cataldo and Shakman paper, attached, where the theory, tests and result of this technology are explained. It has also been well established, that in the modern design of electrical systems, it is a general requirement to include a neutral conductor insulated from ground and that the last standards require the use of 200% current capacity for the neutral bus in cases where harmonical currents are present.
Several designs for bus way systems have been designed in the past. Electrical systems using the paired phase arrangement were described in detail in the U.S. Pat. Nos. 2,287,502, 2,372,267 and 4,008,365, which propose different approaches to obtain designs of bus way systems using the paired phase arrangement for the conductors. These patents propose different options that improve the efficiency, and balance the impedance between the phases using paired phase arrangement, but none of them, however, discloses the encapsulation of each pair with the neutral bus, nor even consider the unbalance impedance between the neutral bus and the phases' conductors. This problem is also present in other commonly used bus way designs, different from the ones that use paired phase arrangements, where unbalanced impedance and unbalanced voltage drops between phases and neutral are frequent. In those cases it's required to use transposition elements in order to compensate the unbalanced voltage drop as was presented in U.S. Pat. No. 4,262,163 issued to Durrell, et al. on Apr. 14, 1981 for a Busway Phase Transposition Assembly.
One of the problems is to topologically arrange the pairs and the neutral bus to obtain balanced impedance and balance voltage drop within phases and neutral conductors in a simple and inexpensive way. As an example of the documentation of the problem, U.S. Pat. No. 2,955,147 issued to Carlson in 1960 is illustrative. The objective of Carlson's patent was to place derivations of the neutral bus in close proximity to every phase, inserting them between the paired buses. Col. 1, lines 62-65. However, this approach is complicated, not compatible with mass production technologies and thermally inefficient.
Another problem is topologically arranging the pairs, the neutral bus and the enclosure in a paired phase system to get the maximal thermal efficiency, the small size and high short circuit capacity of the compact (sandwich type) design, where the bus bars, the duct and the electrical insulation are in intimate contact to provide efficient heat transfer from the bus bars to the enclosure by the way of conduction.
The thermally efficient compact design was described originally in the U.S. Pat. No. 2,350,601 issued to William Frank in 1954, and improved in the U.S. Pat. Nos. 3,555,293, 3,571,488, 3,614,297, 3,644,663, 4,758,172, 4,804,804, 4,945,188 and others, but none of them use the paired phase arrangement in their designs.
Compact (sandwich type) are actually the most common bus way systems used for buildings and general industry, because of their lower cost, compact design and higher short circuit capacity. The paired phase systems are used mostly in particular cases where more efficiency and balanced impedance is required, as in metalwork and automotive industries. Even though the paired phase design provides better technical advantages over the sandwich type, their use is restricted because of their higher cost and non-compact designs.